Process for the preparation of an ironaluminum alloy



6. CABANE ETAL PROCESS FOR THE PREPARATION OF AN IRON-ALUMINUM ALLOY Feb. 14, 1967 Filed Feb. 26, 1965 INVENTOR-S GERHRD Cnanmz PIERRE, mouruRnT Jznu-Fflflncols PETIT csranRn SFHNFORT EHLESSE MHRC ATraRuEY United States Patent The present invention relates to a process for the preparation of an iron-aluminum alloy and, by way of new industrial products, the alloys obtained as a result of the application of said process.

It is known that aluminum can pass into solid solu-- tion in iron up to a proportion by weight of approximately 34%. However, iron-aluminum alloys of the type which have been prepared up to the present time and which permitted of metallurgical processing contained a percentage of aluminum which did not exceed approximately 16 to 18%. The chief difficulty in connection with the high-aluminum alloys obtained by means of conventional processes lay in their brittleness, which accordingly made it diflicult to form objects by machining, such as, for example, the production of thin sheets by rolling, this difiiculty being all the more marked the higher the aluminum content.

The present invention is directed to a process by means of which it is possible to reduce the brittleness of the alloy and to permit the production of parts carrying a proportion of aluminum which may reach approximately 40% by weight.

It has been discovered that the brittleness of Fe-Al alloys as cast was a brittleness of of intergranular structure, but that such brittleness was not solely due, as had been thought hitherto, to the presence of precipitates, for example, of carbides or oxides, at the grain boundaries; instead the separations of grain boundaries which cause the embrittlement of these alloys are mainly due to the existence of mechanical stresses during the cooling of the ingots after casting, the extent of which is due to the poor thermal conductivity of these alloys; the boundary separations are subsequently sensitized by the presence of a precipitate, of a layer of foreign atoms absorbed by the impurities of the constituents, and/ or of an assembly of micro-cavities.

The process in accordance with the present invention is characterized by the steps of preparing a molten mixture of iron, aluminum and one or a number of components or additives which have the effect of reducing brittleness, the aluminum content :being comprised between 16% and 40%, of casting the said mixture under conditions such that internal stresses are very small, the'arrangements referred-to being so chosen as to prevent the occurrence of separations between grain boundaries, and of subsequently destroying the casting structure by a mechanical-working process of hot-state deformation.

It should be noted that among the casting conditions of the process in accordance with the present invention, recourse is bad to a casting temperature which is as close as possible to the temperature of solidification of the alloy, in order to limit the internal stresses which arise during the cooling process and the pre-heating of the ingot-mold when the casting volume is relatively small. Thus, thermal stresses and incipient boundary separations are reduced to an acceptable value.

3,303,561 Patented Feb. 14, 1967 ICC The introduction in very small quantitieswhich are normally less than 1% and preferably less than 0.5 %of addition elements can facilitate the trapping of embrittling impurities.

The said impurities are usually introduced by the iron, since aluminum can be obtained in a high state of purity. An addition of zirconium or of niobium provides appropriate and effective means of trapping the embrittling impurities such as carbon, oxygen and nitrogen. The proportion of addition elements is preferably fixed as a function of the proportion of the impurities present. Accordingly, it has been possible to determine, for example, that the proportion, by Weight, of zirconium must be at least equal to approximately ten times the proportion of carbon-that is to say in an atom-for-atom ratioin order to eliminate the troublesome effects which are due to the presence of carbon, the proportion of which can generally be maintained below 0.02%.

It is apparent that roughing-down may, in certain ;ap plications, prove sufficient to result directly in the finished products. In other cases, machining operations or metallurgical treatments either in the hot state or in the cold state will be necessary.

The addition, in small quantity, of an element such as boron has the effect of improving the intergranular cohesion of the alloy.

Among the new industrial products which are obtained as a result of the application of the method in accordance with the present invention, the binary alloys of iron with aluminum, which may comprise, if necessary, up to 1% of addition elements, containing a proportion by weight of aluminum which may vary between 18 and 31% are particularly valuable. In fact, these proportions correspond at normal atmospheric temperature to alloys which only consist of the phase Fe-Al; above 18% there appears the phase Fe -Al; and above 31%, there appears a precipitate forming the phase Fe-Al The method in accordance with the present invention is not limited, however, to the binary alloys of iron with aluminum in which the brittleness-reducing addition element-s remain in very small quantities, but also applies to those alloys which contain appreciable quantities of other constituents such as beryllium or, in certain cases, silicon. Accordingly, this type of alloy can prOve useful in nuclear applications, as will be brought out more fully hereina ter.

The usual precautions may also be taken with the present invention such as melting and pouring in vacuo, in an inert atmosphere or in free air under a protective fi-ux; the starting materials are preferably as pure as possible. The sequence in which the two main or single constituents are introduced most effectively is that in which iron is fed in first, .followed by aluminum.

The particular features heretofore described have the effect of obtaining a product, as cast, which has only slight brittleness; the remainder of the treatment is carried out in such manner as to obtain good mechanical properties (breaking strength, yield strength, elongation, hardness, etc.) with suitable impact strength. The remainder of the treatment according to the present invention therefore consists in a hot-state mechanical working process which produces the deformation of the as cast product.

During this treatment, or so-called roughingdown process as it will be referred to hereinafter, the casting structure is destroyed; the temperature reached is usually within the range of 600 C. to 1,200 0., and depends on the proportion of aluminum and on the nature and proportion of the additive or additives; the said roughing-down process can be carried out either by extrusion, pressure :forging and/ or rolling; this treatment can be carried out without shocks or without excessively rapid deformations. In

certain forms, the roughing-down process is alone suflicient to provide directly the finished products.

The mechanical working process of deformation in the hot state or roughing-down process, which makes it possible to destroy the casting structure, preferably compris es the steps of covering the ingot which is derived from the casting operation with a metallic jacket, of carrying out the operations of hot-state machine-work on the ingot as fitted with its jacket and of the elimination of the jacket. The jacketing'or cladding process can be effected by any conventional means, but must not be conducive to subsequent weakness at any point in a zone which is subjected to high stresses during the roughing-down process. Such means can include cold hydrostatic cladding, electrolytic coating, metallizing by projection, etc.

One of these subsequent treatments can consist of coldstate deformation by machine-Work or so-called cold work, that is to say, which is carried out at room temperature or at a temperature between room temperature and the temperature of re-crystallization; this machinework process of deformation in the cold state or .cold work which results in strain-hardening, 'may be carried out, for example, either by rolling or drawing, and permits:

The obtainment of products having a smaller thickness. Accordingly, the mini-mum thickness which can be achieved by cold rolling is much smaller than that achieved by hot rolling alone, at least in the case of the rolling machines which are usually employed;

The obtainment of dimensions which are very accurately defined; and

At the expense of a subsequent heat treatment, the adaptation of mechanical properties to a particular purpose.

It is worthy of note that the cold working treatment is made possible by the roughing-down process which has been previously described, even when the aluminum content is higher than In this strain-hardened state and with an iron content which is higher than approximately 75%, the Fe-Al alloy is a disordered solid solution; the said alloy is therefore ferromagnetic and can be employed as a magneticmaterial, especially in the form of thin sheeting or foil.

This property of the Fe-Al alloys which is known and put into application in the case of alloys having an iron content higher than 84%, has been confirmed in the case of alloys having an iron content which ranges from 75% to 84% by weight.

The Fe-Al alloys having an iron content within the range of 75 to 84% in accordance with the present invention are therefore new magnetic materials which constitute new industrial products; the said alloys have the advantage of a density which is lower than that of other iron-base magnetic alloys and which is also lower than that of such Fe-Al magnetic alloys as have already been prepared heretofore; moreover, the oxidation resistance of the alloys in accordance with the present invention is very high, and higher than that of the Fe-Al alloys of the prior art, inasmuch as the aluminum content is higher.

Taking into account the small neutron-absorption crosssection thereof, the alloys in accordance with the present invention may, therefore, effectively replace in certain cases cobalt alloys with a view to constructing the magnets employed in nuclear reactors.

For the purpose of improving the mechanical characteristics of the Fe-Al alloy, it is of advantage to subject the said alloy, either directly after the roughingdown process or after the cold working process, to a heat treatment which has the effect of modifying the distribution of impurities as well as the structure of the alloy; the said heattreatment may be of any suitable known type which is adapted to the desired modifications, while the temperature must obviously not exceed that at which the grain would grow again to a large size; this treatment may accordingly consist, for example, of an annealing process or a drawing of temper. Inasmuch as the structure which is then formed is not brittle, the treatment may subsequently be followed by a further mechanical treatment, either in the hot state or in the cold state or both, which is in turn followed by a heat treatment; the cycle may also be repeated a number of times.

If the alloy is intended to be employed as a structural material in either a. medium-temperature or high-temperature reactor, it may prove desirable for the purpose of, ensuring that the mechanical behavior of the said material during operation is stabilized to the maximum extent within the shortest possible time, to carry out the said heat treatment as a preliminary step, at least at the maximum temperature which is subsequently reached in the reactor channel Generally speaking, the Fe-Al alloys in accordance with the present invention are characterized by remarkable oxidation resistance which is greater than that of stainless steel in the case of high aluminum contents (over 18%, for example), and which is essentially due to the fact that the external surface of the alloy is coated with a self-protecting film of oxide.

Inasmuch as aluminum is characterized by a low neutron absorption cross-section, the alloys in accordance with the present invention may also be contemplated for use as structural material in nuclear reactors, especially as cladding material for fuel elements. For equal thickness of cladding, the neutron absorption of the alloy in accordance with the present invention is distinctly lower than in the case of stainless steel and the yield strength at high temperature, for example, between 450 C. and 700 C., is distinctly higher than that of stainless steel.

The Al-Fe alloy, which may in certain cases contain beryllium or even silicon, therefore constitutes a structural material which may be employed in nuclear reactors, for example, as cladding material, especially in high-temperature reactors, and may be employed in those cases in which stainless steel or beryllium are not suitable for use, the former on account of its very high neutron-absorption capacity, the latter on account of its brittleness, of its low creep strength above 600 C., of the swelling of cans or jackets as a result of the formation of helium pockets, and finally of its unduly low corrosion resistance when hot, especially in CO at 600 C.

By way of comparison, a reactor which is designed for the use of uranium oxide (natural uranium) as fuel, for the use of CO as a coolant gas at a temperature of 600 C. and a pressure of 60 kg./cm. and for the use of cylindrical fuel elements 15 'mm. in diameter, could not operv.ate with a can of stainless steel having a thickness of 0.2

mm. (this thickness being the limit value established for reasons of safety); the reactivity loss which results from the cladding is then in fact 0.087 per hundred thousand,

that is to say, more than double the available margin for certain proportion of aluminum, to avoid the use of enriched uranium. The said proportion of aluminum must be greater than 20% in order to ensure that this should be so; in the case of a binary iron-aluminum alloy and 18-8 stainless steel, the cross-sections 2 of the cladding tubes are as follows:

18-8 stainless steel 2:0.245 emf Binary Fe-Al alloy containing 20% by weight of aluminum 2:0.142 cm. Binary Fe-Al alloy containing 30% by weight of aluminum 2:0.115 cm.

In the case of a ternary alloy in which the third constituent has a low neutron absorption cross-section, the percentage of aluminum contained in the alloy may be decreased while at the same time decreasing the global cross-section of the alloy; 1% by weight of beryllium is in fact equivalent from the viewpoint of neutron absorption cross-section to 2% by Weight of aluminum.

Accordingly, it is an object of the present invention to provide a process for the manufacture of an alloy containing principally iron and aluminum of which the proportion of aluminum may be increased considerably without the attendant difficulties encountered heretofore.

Another object of the present invention resides in the provision of a process for producing an iron-aluminum alloy in which thealuminum content may be increased to a range above that normally feasible heretofore, without producing a product of which the brittleness is so great as to preclude any subsequent machining operations.

Another object of the present invention resides in the provision of a novel iron-aluminum alloy containing, by weight, approximately 16 to 40% of aluminum of which the brittleness is relatively low and which permits of subsequent hot or cold working operations.

A further object of the present invention resides in the provision of Fe-Al alloys in which the brittleness is controlled to a degree not realizable heretofore.

A further object of the present invention resides in the provision of a process for the manufacture of iron-aluminum alloys in which the thermal stresses are reduced and incipient boundary separations are controlled to fall within acceptable values.

A still further object of the present invention resides in a novel alloy principally containing iron and aluminum and having a relatively high proportion of aluminum which has magnetic properties and may be produced in the form of thin sheeting or foil.

Another object of the present invention resides in the provision of a process for the manufacture of an ironaluminum alloy which permits of obtaining very small thicknesses, accurate dimensions, and cold working treatments as well as subsequent heat treatments.

A further object of the present invention resides in the provision of a process for producing a low density iron-base magnetic alloy and in the resulting product which not only exhibits such low density properties, but also an oxidation resistance that is considerably higher than that of other iron-aluminum alloys as well as stainless steel.

Still another object of the present invention resides in the provision of a process for producing an ironaluminum alloy having neutron absorption properties that are distinctly lower than those of stainless steel and having a yield strength that is considerably higher than that of stainless steel.

Still a further object of the present invention resides in the provision of a process for producing an ironaluminum alloy and the alloy resulting from such process which may be used in nuclear reactors and has such properties and characteristics as to obviate the need for enriched fuels.

The present invention will be more clearly understood from a perusal of the following description of a number of examples of practical application of the process in accordance with the present invention for the preparation of an iron-aluminum alloy, the said examples being given only for illustrative purposes and without implying any limitation on the present invention. The single figure of the accompanying drawing shows a diagram illustrating the corrosion of an alloy in accordance with the present invention in a carbon dioxide gas atmosphere as compared to that of a stainless steel under similar conditions.

EXAMPLE I The alloy to be produced has the following composition:

Electrolytic iron 3 kgs. (74.92%). Aluminum of 99.99% purity 1 kg. (24.98%). Zirconium 4 grams (0.1%).

(a) Melting and casting.Th'e 3 kilograms of electrolytic iron are melted and brought to a temperature of 1,600 C. in a vacuum of the order of 10 millimeters Hg; aluminum 'of 99.99% purity is then added thereto, followed by zirconium; the temperature is reduced to 1,450 C. and the molten mixture is poured off in vacuo, again of about 10* mm. Hg, into an ingotrnold which has been heated to 620 C.

Finally, the cooling rate is limited to approximately 50 C. per hour. It should be noted in passing that preheating is of course necessary in this example only on account of the fact that the casting mass employed in this example is small.

(b) Roughing-down.The ingot which is obtained from step (a) above after cooling is fitted with a metallic jacket, for example, of ordinary steel (XC 12 or XC 35 in particular). The covering of the ingot may be carried into effect by means of any one of the methods of conventional cladding, for example, by welding a sheet which has previously been wrapped around the ingot, by cold-state hydrostatic cladding, etc. The thickness of the jacket is obviously designed so that the subsequent mechanical treatments permit a thickness to remain which is such that there is no danger of tearing. This thickness was of the order of 2 mm. in the example described.

The composite work-piece formedby the ingot which is covered with its jacket is subjected to a series of rolling passes at 1050 C., each pass necessarily resulting in a reduction in thickness which is sufficient to work-harden the metal right through.

The presence of the jacket makes it possible to facilitate the surface flow of the alloy and permits of deformations which the ingot would not withstand if it were treated in the uncovered state.

In the example referred-to, each pass resulted in a reduction in thickness of 2 mm., while between two successive passes, there was carried out a reheating for a period of two minutes, thereby bringing the temperature back to 1050 C. The thickness of the composite workpiece can thus be reduced without difficulty to approximately 2 mm. It is apparent that the reheating treatment is only necessary on account of the fact that the temperature of the work-piece falls substantially as a result of the small dimensions of the latter.

The composite work-piece can then be freed of its steel jacket (the thickness of which has obviously been substantially reduced to the same extent as those of the workpiece) by dilferent methods. The jacket, which in the example described only remains in the form of a film of the order of a few tenths of a millimeter, can be, for example:

Detached by machine-cutting of the jacket along one of the sides of the casing,

Destroyed by chemically dissolving the jacket in a mixture of 50% nitric acid and 50% water (the ironaluminum alloy having good resistance to attack by dilute nitric acid),

Destroyed by selective oxidation of the jacket by air heating or heating in an oxidizing atmosphere.

(0) Cold working-The alloy which is thus obtained may be subjected to subsequent mechanical operations which result in limited deformations, for example, deformation by rolling at room temperature with annealing treatments between successive rolling passes.

EXAMPLE II (a) Melting and casting.A cast is prepared under conditions which are similar to those of Example I starting with 2.9 kilograms of electrolytic iron, 1.1 kilograms of aluminum and 4 grams of zirconium. The temperature is then raised to a few tens of degrees above the solidification temperature (or liquidus temperature) of the alloy and the latter is poured off in vacuo into a preheated ingot-mold. The cooling process is then carried out as in Example I. The alloy which is thus cast has the following composition by weight:

. Percent Iron 72.2 Aluminum 27.7 Zirconium 0.1

A In addition thereto, analysis shows traces of carbon, nitrogen, phosphorus and sulphur in the following proportions:

Percent Carbon 0.01 Nitrogen 0.01 Phosphorus 0.002 Sulphur 0.002

(b) Rughing-d0wn.The ingot thus produced is capable of undegoing lathe turningwork when useis made of tools having great hardness such as tungsten-carbide tools. The quality of machining is improved by maintaining the alloy at 400 C. during the machining operation.

The said machining operation may not be necessary in the case of certain surface conditions and when the roughing-down operation consists in a rolling process which can be performed after cladding according to a procedure which is similar to that described in the previous example. However, such a machining operation is necessary for the purpose of shaping the ingot when the treatment involves extrusion of the jacketed ingot.

When the extrusion process is intended to result in a full rod or slug, the lathe turning operation is performed with a view to obtaining a cylinder having a rounded front end. The work-piece which is thus machined is covered by means of any conventional process with a steel jacket having a shape which is adapted to that of the said work-piece and a thickness of a few millimeters. It may be useful to replace mild steel by other metals or alloys such as iron-aluminum alloys containing a low percentage of aluminum, which have the advantage of better oxidation resistance and, in certain cases, nickel or cupronickel.

The composite part which is thus obtained is then pressextruded at 950 C. At this temperature, it is possible to reach an extrusion ratio of the order of 1:30, or in other words, it is possible to prepare rods of 11 mm. diameter from machined ingots of 60 mm. diameter.

A similar process makes it possible to obtain tubes having a thickness which is less than one millimeter. In this case, the lathe turning operation is performed with a view to producing a hollow cylinder which is then clad both internally and externally.

After extrusion, the separation of the alloy and its steel jacket can be carried out in accordance with any one of the processes which have already been referred toin Example 'I, for example, by chemical dissolution in a solution composed of 50% water and.50% nitric acid which rapidly dissolves the jacket, by oxidation of the jacket, by air heating or in an oxidizing atmosphere. In the latter case, the jacket disappears whereas the alloy is not attacked by virtue of its high resistance to oxidation.

(0) Cold w0rking.-The extruded product obtained may, in certain cases, be employed as it stands, inasmuch as it has a good surface to. finish. However, it may, if necessary, be subjected to a further cold working treat ment and may, for example, be threaded on a threadcutting lathe. In fact, the grain size after extrusion is reduced to 20 or 30 microns and accordingly permits of machining.

The part which has been either machined or extruded may besubjected to a heat treatment for a period of 8 one hour at 800 C.; after this heat treatment, the extruded product has the following characteristics:

Tempera- Ultimate Yield Elongation titre, Tensile Strength, at Fracture, 0. Strength, kgsJmm. Percent kgsJmrn.

I 1 Brittle fracture.

EXAMPLE III The same operations as in Example II (melting, casting, machiningQjacketing, extrusion and elimination of the jacket) have also been applied to an alloy cont-aining 25% aluminum by Weight, the composition of which is as follows:

Percent Iron 74.9' Aluminum 25.0

Zirconium 01 and which shows traces of impurities in the following proportions:

- I A Percent Carbon 0.01

Nitrogen -2. 0.01 Phosphorus 0.002 Sulphur 0.002

After heat treatment at 800 C., the product obtained has the characteristics which are given in the table below:

Tempera- Ultimate Yield Elongation ture, Tensile Strength. at Fracture, 0. Strength, kgs./mrn. Percent kgs/mmfl 1 Brittle fracture.

sents the oxidation (expressed as increase in weight per unit area), against time (expressed in hours) of two materials in a carbon dioxide atmosphere at 700 C. under a pressure of 60 kgs./cm. The curve (I) corre-- sponds to the iron-aluminum alloy in accordance with Example III herein. Curve. (II)v corresponds to an 18- 12 niobium-stabilized stainless steel which is known for its good resistance to. corrosion by carbon. dioxide gas at high temperature. It may be readily seen from this figure that, at the end of a period of exposure of 5,500 hours, the corrosion of the iron-aluminum alloy is less than one half that of stainless steel.

EXAMPLE IV (a) Melting and casting.An alloy containing 79.6%

iron, 17.2% aluminum, 2.8% beryllium and 0.4% Zirconium is prepared from the following constituents:

Iron ..-kgs 3 Aluminum kgs 0.650 Beryllium kgs 0.105 Zirconium -grams 15 The melting and casting operations are carried out as in the previous examples; in the as cast state, this alloy has the following properties:

Grain size approximately 0.15 mm. Brinell hardness A=320.

(b) Roughing-down.The ingot is rolled at a temperature of 1050 C. in passes which each result in a reduction in thickness of 1 mm. to a final thickness of 2 mm.; in this state, the alloy has a Brinell hardness A=330.

Thereafter, a heat treatment at 1,l C. makes it possible to reduce the Brinell hardness number to 260.

EXAMPLE V (a) Melting and casting.The same operations of melting and casting are applied to an alloy containing 25% aluminum having the following composition by weight:

Percent Iron 74.9

Aluminum 25 Zirconium 0.1

and impurities in the form of traces:

Percent Carbon 0.01 Nitrogen 0.01 Phosphorus 0.002 Sulphur 0.002

(b) Roughing-downJwt-state def0rmati0n.Rolling passes are effected at 1,050 C. and a reheating treatment is performed between each rolling pass for a period of two minutes.

A reduction value of less than 90% can be obtained with final thicknesses of the order of one millimeter.

(c) Cold-stale def0rmati0n.After hot rolling, the rolling treatment can be repeated at room temperature.

It is accordingly possible as a result of cold rolling to obtain reduction values of 50%.

After rolling, the Vickers hardness number of the product is 500 HV; heat treatments by annealing at 950 C. make it possible to reduce this hardness number to 280 HV.

EXAMPLE VI The same operations as in Example II (melting, casting have been applied to an alloy having the following composition:

7 Percent Iron 68.9

Aluminum 31 Zirconium 0.1

and impurities of the same order as in Examples II and III.

The product obtained has the following characteristics:

Ultimate Yield Elongation Temperatensile strength, at rupture, ture, C. strength, kgs./mm. percent kgs/mm.

it possible to approach the limit of solubility of aluminum in iron (34% approximately) while retaining good mechanical properties. If such mechanical properties are not essential requirements, a small precipitation of aluminum is permissive at the expense of a very substantial reduction of mechanical characteristics, thereby making it possible to reach a proportion of approximately 40%.

It is wholly apparent that the scope of the present invention extends not only to the process which has just been described and to all alternative forms thereof which are within the scope of equivalency thereof, but also, by way of new industrial products, to the alloys which are obtained as a result of the application of the process in accordance with the present invention.

Thus, while we have described several specific examples in accordance with the present invention, it is obvious that the same is not limited thereto, but is susceptible of numerous changes and modifications within the scope of a person skilled in the art, and We therefore do not wish to be limited to the details described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. A process for the preparation of an iron-aluminum alloy consisting essentially of between greater than 18% and about 40% by weight of aluminum, up to 1% by weight of an additive selected from the group consisting of zirconium, niobium, titanium, yttrium, the rare earths, boron and mixtures thereof and the balance iron, comprising the steps of:

melting said iron,

incorporating said additive and said aluminum into said molten iron,

casting with only a sight amount of superheat to produce, after solidifcation and cooling of the alloy, an ingot thereof, and hot working said ingot. 2. The process according to claim 1, wherein said'casting temperature is less than 50 C. above said temperature of solidification and said casting operation is carried out in a preheated ingot mold.

3. The process according to claim 1, wherein the ingot obtained from said casting step is covered with a metallic jacket to clad the same, the clad ingot being subjected to said step of hot state mechanical working and deformation, and thereafter said cladding jacket is removed from the alloy.

4. A process for the preparation of a ternary ironaluminum base alloy consisting essentially of between greater than 18% and to about 40% by weight of aluminum, up to 2.8% by weight of berylliumand the balance iron, comprising the steps of:

melting said iron, adding said aluminum and said beryllium to said molten lI'OIl,

casting with only a slight amount of superheat to produce, after solidification and cooling of the alloy, an ingot thereof,

and hot working said ingot.

5. A process for the preparation of an iron-aluminum base alloy consisting essentially of between greater than 18% and about 40% by weight of aluminum, up to 1% 'by weight of an additive selected from the group consisting of zirconium, niobium, titanium, yttrium, the rare earths, boron and mixtures thereof, up to 2.8% by weight of beryllium and the balance iron, comprising the steps of:

melting said iron, 1

adding said additive, said aluminum and said beryllium to said molten iron,

casting with only a slight amount of superheat to produce, after solidification and cooling of the alloy, an ingot thereof,

and hot working said ingot.

6. A process for the preparation of a binary iron-aluminum alloy consisting essentially of between 30% and about 40% by weight of aluminum and the balance iron, comprising the steps of:

melting said iron,

adding said aluminum to said molten iron,

casting with only a slight amount of superheat to produce, after solidification and cooling of the alloy, an ingot thereof,

and hot working said ingot.

7. A process for the preparation of an iron-aluminum alloy consisting essentially of between greater than 18% and about 40% by weight of aluminum, up to 1% by weight of an additive selected from the group consisting of zirconium, niobium, titanium, yttrium, the rare earths, boron and mixtures thereof and the balance iron, comprising the steps of:

melting said iron,

incoporating said additive and said aluminum into said molten iron,

casting at a temperature less than 50 C. above the temperature of solidification of the alloy into a preheated ingot mold to produce, after solidification and cooling of the alloy, an ingot thereof, said melting and casting steps being carried out in an inert atmosphere,

covering said ingot with a metallic jacket to clad the same,

- destroying the cast structure of said ingot by subjecting it to a progressive deformation treatment in the hot state within a temperature range of from about 600 C. to 1200 C.,

:and thereafter removing said cladding jacket from said alloy.

8. The process according to claim 7, comprising the additional step of further deforming the alloy obtained by means of said progressive deformation treatment by machine working said alloy at a temperature of between ambient temperature and about 600 C.

9. The process according to claim 7, wherein said cool ing is carried out at a rate of approximately 50 C. per hour.

10. A binary iron-aluminum alloy consisting essentially of between 30% and about 40% by weight of aluminum and the balance iron.

11. An iron-aluminum alloy consisting essentially of between greater than 18% and about 40% by weight of aluminum, up to 1% by weight of an additive selected from the group consisting of zirconium, niobium, titanium, yttrium, the rare earths, boron and mixtures thereof and the balance iron.

12. The alloy of claim 11, wherein said additive is zirconium in an amount of about 0.1% by weight.

13. A relatively thin sheet composed of the iron-aluminum alloy of claim 11.

14. The iron-aluminum alloy of claim 11, wherein said aluminum is present in an amount between greater than 18% and about 34% by weight.

15. A ternary iron-aluminum base alloy consisting essentially of between :greater than 18% and about 40% by weight of aluminum, up to 2.8% by weight of beryllium and the balance iron.

16. An iron-aluminum base alloy consisting essentially of between greater than 18% and about 40% by weight of aluminum, up to 1% by weight of an additive selected from the group consisting of zirconium, niobium, titanium, yttrium, the rare earths, boron and mixtures thereof, up to 2.8% by weight of beryllium and the balance iron.

17. The alloy of claim 16, wherein said additive is zirconium.

18. A ternary iron-aluminum base alloy consisting essentially of between greater than 18% and about 40% by weight aluminum, from about 1% to about 2.8% by Weight of berylli np and the balance iron.

19. An iron-aluminum base alloy consisting essentially of between greater than 18% and about 40% by weight of aluminum, up to 1% by weight of an additive selected from the group consisting of zirconium, niobium, titanium, yttrium, the rare earths, boron and mixtures thereof, from about 1% to about 2.8% by weight of silicon and the balance iron.

20. A ternary iron-aluminum base alloy consisting essentially of between greater than 18% and about 40% by weight of aluminum, at least 1% by weight of a material selected from the group consisting of beryllium and silicon andthe balance iron.

21. An iron-aluminum base alloy consisting essentially of between greater than 18% and about 40% by weight of aluminum, up to 1% by weight of an additive selected from the group consisting of zirconium, niobium, titanium, yttrium, the rare earths, boron and mixtures thereof, at least 1% by 'weight of a material selected from the group consisting of beryllium and silicon and the balance iron.

22. An iron-aluminum alloy consisting essentially of between greater than 18% and 31% by weight of aluminum, up to 1% by weight of an additive selected from the group consisting of zirconium, niobium, titanium, yttrium, the rare earths, boron and mixtures thereof and the balance iron, said alloy consisting solely of the Fe-Al phase.

23. Alprocess for the preparation of an at least binary iron-aluminum alloy consisting essentially of between greater than 18% and about 40% by weight of aluminum and the balance iron, said alloy being characterized by a relatively low brittleness permitting machining operations, comprising the steps of:

melting said iron,

adding said aluminum to said molten iron,

casting at a temperature less than 50 C. above the temperature of solidification of the alloy into a preheated ingot mold to produce, after solidfication and cooling, an ingot thereof,

and destroying the cast structure of said ingot by hot state mechanical working and deformation.

24. The process according to claim 23, whereinsaid iron-aluminum alloy consists essentially of between greater than 18% and about 34% by weight of aluminum and the balance iron and wherein said hot state mechanical working and deformation is carried out at a temperature of between 950 and 1050 C. V

25. The process according to claim 23, wherein the destruction of the cast structure of said ingot is carried out by means of a progressive deformation treatment in the hot state within a temperature range of from about 600 C. to 1200 C.

26. The process according to claim 23, wherein the ingot obtained from said casting step is covered with a metallic jacket to clad the same, the clad ingot being subjected to said step of hot state mechanical working and deformation, and thereafter said cladding jacket is removed from the alloy.

27. The process according to claim 26, comprising the additional step of further deforming the alloy obtained by means of said progressive deformation treatment by machine working said alloy at a temperature of between ambient temperature and about 600 C. and wherein the ingot is machined prior to-said cladding.

28. The process according to claim 27, wherein said step of machine working is followed by a step of heat treatment of the alloy.

29. The process according to claim 23, wherein said melting and casting steps are carried out in an inert atmosphere.

30. The process according to claim 23, wherein said cooling is carried out at a rate of approximately 50 C. per hour.

(References on following page) 13 1 14 References Cited by the Examiner 2,859,143 9/ 1958 N achman et a1 1482 3,026,197 3/ 1962 Schramm 75--124 UNITED STATES PATENTS 3,144,330 8/1964 Storchheim 75 124 X 2,768,915 10/1956 Nachman et a1. 75124 X 2,804,387 57 M0rgan et 1 75 124 5 JOHN F. CAMPBELL, Przmary Exammer. 2,846,494 8/1958 Lindenblad 75124 X P. M. COHEN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,303,561 February 14, 1967 Gerard Cabane et al It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 9, the last TABLE, second column, line 4 thereof,

" 22" should read 22 Signed and sealed this 11th day of November 1969.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. A PROCESS FOR THE PREPARATION OF AN IRON-ALUMINUM ALLOY CONSISTING ESSENTIALLY OF BETWEN GREATER THAN 18% AND ABOUT 40% BY WEIGHT OF ALUMINUM, UP TO 1% BY WEIGHT OF AN ADDITIVE SELECTED FROM THE GROUP CONSISTING OF ZIRCONIUM, NIOBIUM, TITANIUM, YTTRIUM, THE RARE EARTHS, BORON AND MIXTURES THEREOF AND THE BALANCE IRON, COMPRISING THE STEPS OF: MELTING SAID IRON, INCORPORATING SAID ADDITIVE AND SAID ALUMINUM INTO SAID MOLTEN IRON, CASTING WITH ONLY A SIGHT AMOUNT OF SUPERHEAT TO PRODUCE, AFTER SOLIDFICATION AND COOLING OF THE ALLOY, AN INGOT THEREOF, AND HOT WORKING SAID INGOT.
 23. A PROCESS FOR THE PREPARATION OF AN AT LEAST BINARY IRON-ALUMINUM ALLOY CONSISTING ESSENTIALLY OF BETWEEN GREATER THAN 18% AND ABOUT 40% BY WEIGHT OF ALUMINUM AND THE BALANCE IRON, SAID ALLOY BEING CHARACTERIZED BY A RELATIVELY LOW BRITTLENESS PERMITTING MACHINING OPERATIONS, COMPRISING THE STEPS OF: MELTING SAID IRON, ADDING SAID ALUMINUM TO SAID MOLTEN IRON, CASTING AT A TEMPERATURE LESS THAN 50%*C. ABOVE THE TEMPERATURE OF SOLIDIFICATION OF THE ALLOY INTO A PREHEATED INGOT MOLD TO PRODUCE, AFTER SOLIDFICATION AND COOLING, AN INGOT THEREOF, AND DESTROYING THE CAST STRUCTURE OF SAID INGOT BY HOT STATE MECHANICAL WORKING AND DEFORMATION. 